Opto-electronic devices refer to, in a broad sense, devices that convert light energy into electric energy or vice versa and include, for example organic electroluminescent devices, solar cells, transistors, and the like.
Among other things, recent advances in Flat-Panel Display (hereinafter, referred to as FPD) technology have focused a great deal of attention on organic electroluminescent devices.
Liquid crystal displays (LCDs) make up the largest proportion of current FPDs, comprising more than 80% of the FPD market, due to significant development in related technologies. However, such LCDs suffer from critical disadvantages such as low response speeds exhibited by large screens having a size of more than 40 inches, narrow viewing angles, and the like. As such, there is a need for the development of novel displays in order to overcome such disadvantages.
Organic electroluminescent (EL) displays have received a great deal of interest among FPDs as the only display mode satisfying the requirements for the next-generation of FPDs. For example, organic EL displays can offer advantages such as low driving voltage, self luminescence, thin film-type, wide viewing angles, rapid response speed, high contrast and low cost.
Currently, intensive and extensive research in the area of opto-electronic devices including such organic electroluminescent (EL) devices is directed to the formation of conducting polymer films, in order to increase device efficiency via smooth transportation of electric charges generated from electrodes, i.e., holes and electrons, to the inside of the opto-electronic devices.
In particular, the organic electroluminescent (EL) device is an active luminescence-type display utilizing phenomena in which the application of electric current to a fluorescent or phosphorescent organic compound thin film (hereinafter, referred to as organic film) leads to the generation of light as electrons and holes combine in the organic film. To improve device efficiency and reduce operating voltage, such an organic electroluminescent (EL) device generally has a multi-layer structure including a hole-injection layer, a light-emitting layer and an electron-injection layer containing conducting polymers, instead of a single light-emitting layer alone as the organic layer.
Further, such a multi-layer structure can be simplified by fabricating one layer to perform multi-functions while removing the respective corresponding layers. The simplest structure of the EL device is made up of two electrodes and an organic layer disposed therebetween that performs all the functions including light emission.
However, in fact, in order to increase the luminance of the device, an electron-injection layer or a hole-injection layer should be introduced into an electroluminescent assembly.
A large number of organic compounds having electric charge (holes and/or electrons) transporting properties are known and can be found in a variety of scientific journals and literature. A general overview of such species of materials and uses thereof is found, for example, in European Patent Publication No. 387 715, and U.S. Pat. Nos. 4,539,507, 4,720,432 and 4,769,292.
Poly(3,4-ethylenedioxythiophene) (PEDOT)/poly(4-styrenesulfonate) (PSS), commercially available from Bayer AG under name of Baytron-P, is a representative organic compound capable of transporting electric charges currently used in the form of an aqueous solution in soluble organic EL devices. This compound is widely used in the fabrication of organic EL devices for the formation of the hole-injection layer on an indium tin oxide (ITO) electrode via spin coating. PEDOT/PSS, a hole-injecting material, has a structure of Formula 1 below:

A conducting polymer composition of PEDOT/PSS in which a conducting polymer of poly(3,4-ethylenedioxythiophene) (PEDOT) is doped with a polyacid of poly(4-styrenesulfonate) (PSS) can be used to form the hole-injection layer. Due to its high water-uptake, however, it is difficult to use PEDOT/PSS in cases requiring the removal of water. In addition, because the conducting polymers are simply doped on PSS polymer chains, PEDOT/PSS undergoes dedoping from heat generated in the devices, thus making it difficult to create stable devices. Further, the PSS portion, simply doped on PEDOT, decomposes via reactions with electrons, thus liberating materials such as sulfate, which in turn may diffuse into an adjacent organic film, for example, the light emitting layer. Such diffusion of hole-injection layer derived-materials into the light emitting layer causes exciton quenching and leads to decreased efficiency and life-time of the organic electroluminescent device. In addition, it can be difficult to control the ratio of the conducting polymer when using PEDOT/PSS and thus it is difficult to obtain polymers having the same properties.
Therefore, in order to achieve satisfactory efficiency and life-time in opto-electronic devices such as organic electroluminescent devices, there is an increasing need for the development of a novel conducting polymer and a composition thereof.